Uses of colon in javascript

Question

Assign object literal properties var foo = { bar : 'hello'};
Ternary var cats = happy ? "yes" : "no";
Label a statement outer_loop: for(i=0; i<3; i++)
What else?

I'm poking through a sharepoint 2010 file and I keep running into this syntax

someFunction: ;

For instance, there is a file where the following function is declared near the top:

function ULSqvN() {
    var o = new Object;
    o.ULSTeamName = "SharePoint Portal Server";
    o.ULSFileName = "SocialData.js";
    return o;
}

and then later in the file we find the following

PageUrlNormalizer = function () {
    ULSqvN: ; //<---------------- This guy here --------------------------
    try {
        this._url = _normalizedPageUrlForSocialItem
    } catch (a) {
        this._url = ""
    }
};

What is this doing?

jsFiddle with full file. This same ULSqvN: ; occurs 47 times in the file.

edit: Added full code.

PS: Consensus seems to be that the sharepoint use of colon is "not actual javascript, possibly used as a marker for some external purpose". The browser sees it as a vestigial label and so causes no errors. Thanks for all the replies, I have left the actual uses at the top so that the question contains the appropriate answers. question about same code

You point it out yourself: it's a label. It is likely automatically generated by the obfuscator (but I don't have a reason as for "why"). And, as always, the awful atrocity that is MS JS is showing it's ugly head... ever take a look at the Communicator stuff? :) — , Jan 20 '12 at 19:38
A label defined like that can't be used. It will be `undefined` after the semicolon: http://jsfiddle.net/ThinkingStiff/3F7UY/. The only other use I could think of is a tracing or debugging tool, or perhaps unit testing. Maybe the coder was using them as comments?! — ThinkingStiff, Jan 20 '12 at 19:41
@Sinetheta Would a *sane* programmer use "ULSqvN"? The SP stuff has a *bunch* of mangling (with even more cryptic names in places), so yes, there is likely a processing tool being applied. — , Jan 20 '12 at 19:42
@ThinkingStiff lol, thanks. Although that would be hilarious, it wouldn't be the saddest thing I've found baked into Sharepoint. — Sinetheta, Jan 20 '12 at 19:43

score 8 · Accepted Answer · edited May 23 '17 at 10:28

8

It has no purpose javascript-wise (since in javascript you would only label something that you can continue or break), it might be used as a some kind of comment or marker for some parsing script. At worst it's just dead code with no purpose whatsoever.

Edit: looks like sharepoint uses it for some diagnostic information: What does this Javascript code do?

edited May 23 '17 at 10:28

Community

1
1

answered Jan 20 '12 at 19:35

Esailija

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You win the check-mark unless someone can figure out a use for this code. – Sinetheta Jan 20 '12 at 19:44
@Sinetheta I have clarified the "marker for some parsing script" part :D The point about being completely dead code for javascript itself still holds though – Esailija Jan 20 '12 at 19:47
thanks for finding that question "What does this Javascript code do?" wasn't my first search when I went looking for answers ;) – Sinetheta Jan 20 '12 at 20:52

score 3 · Answer 2 · edited May 23 '17 at 12:15

3

These are labels. Usually they are used to break out of several nested loops at once.

Example

function foo ()
{
    dance:
    for(var k = 0; k < 4; k++){
        for(var m = 0; m < 4; m++){
            if(m == 2){
                break dance;
            }
        }
    }
}

Credit: this answer.

edited May 23 '17 at 12:15

Community

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answered Jan 20 '12 at 19:17

Sergio Tulentsev

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sorry, I should have included more code. Shouldn't a label immediately proceed a loop of some kind? Mine is just hanging out on its lonely, immediately followed by a semi-colon – Sinetheta Jan 20 '12 at 19:22
@Sinetheta: yeah, that doesn't make sense. Maybe it's just abandoned code? :) – Sergio Tulentsev Jan 20 '12 at 19:23
Wouldn't that function the same way if `dance:` had a semicolon after it? Maybe the coder of the OPs code didn't know any better. – ThinkingStiff Jan 20 '12 at 19:34
@ThinkingStiff Since this is a source file from sharepoint 2010 I'm really hoping it's valid useful js – Sinetheta Jan 20 '12 at 19:37
@Sinetheta Wow, I was wrong. It's actually broken: http://jsfiddle.net/ThinkingStiff/3F7UY/. `Uncaught SyntaxError: Undefined label 'dance'`. After the semicolon it can't be used. – ThinkingStiff Jan 20 '12 at 19:39

score 2 · Answer 3 · answered Jan 20 '12 at 19:18

2

It is am empty label, and then an empty statement. (I can't see any good reason for this - unless there is something later in the function that wasn't included here, that needs the label to break out of a loop within that function.)

answered Jan 20 '12 at 19:18

ziesemer

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And the label name just happens to be the name of a function? – Sinetheta Jan 20 '12 at 19:30
@Sinetheta - Yes. This doesn't make any sense to me. The script would execute the same both with and without the labels. – ziesemer Jan 20 '12 at 19:36
Thanks for your reply, sounds like that is the consensus – Sinetheta Jan 20 '12 at 20:55

score 1 · Answer 4 · answered Jan 20 '12 at 19:22

1

The third usage is to label a statement for use with a break or continue statement. See the spec.

answered Jan 20 '12 at 19:22

Larry K

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thanks, forgot to include that. Still trying to figure out what's going on in this file though. It's straight from Sharepoint 2010 so I'm assuming it does something useful. – Sinetheta Jan 20 '12 at 19:30

Uses of colon in javascript

4 Answers4

Example